Pool-type discharge device



Oct. 10, 1939. J. H. HUTCHINGS POOL-TYPE DISCHARGE DEVICE Filed Feb. 23, 1938 Invent or John H. Hutchirgs,

by W Hi5 ttorneg.

Patented Oct. 10, 1939 PATENT OFFICE POOL-TYPE DISCHARGE DEVICE John H. Hutchings, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 23, 1938, Serial No. 191,897

3 Claims.

This invention relates to discharge devices of the type which employ a pool-type cathode, such as a cathode consisting of mercury. The features described and claimed in the following constitute improvements on the invention of U; 5. application Serial No. 191,855, filed Feb. 23, 1938, in the name of L. D. Miles.

It is a primary object of the present invention to provide a controllable pool-type discharge device which is of simple and economical construction and which is adapted for high voltage operation. More specifically, it is my object to make available a device of the type specified which is not subject to arc-back even when used .5 in circuits involving voltages of 30,000 volts or more.

In a preferred embodiment of the invention, I accomplish the foregoing objects by the use of an elongated metal envelope enclosing the anode 20 and cathode of the device and having a series of cooperating sheet metal baifies supported from its inner wall surfaces at spaced points along the envelope axis. These are so formed and located as to shield the anode of the device from any di'#- 5 rect exposure to the cathode, while at the same time providing an adequate path for the discharge current.

The features of novelty which I desire'to protect herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 is a longitudinal sec- 5 tion of a discharge device suitably embodying the invention; Fig. 2 is a transverse section taken on line 22 of Fig. 1; Fig. 3 is a sectional view illustrating the essential elements of a modified embodiment of the invention and Fig. 4 is a trans- 40 verse section taken on line 4-4 of Fig. 3.

Referring particularly to Fig. 1, I have shown an elongated discharge envelope comprising two concentric metal cylinders 10 and H which are so spaced as to form a water jacket between them.

45 The inner cylinder is distorted at its ends so as to fit tightly within the outer cylinder, to which it is circumferentially joined, for example, by welding. Inlet and outlet connections for cooling water are respectively placed at the bottom and top 50 of the outer cylinder as indicated at 12 and 13. The ends of the cylinder are closed by means of transverse headers l5, and 16, which are provided with peripheral flanges hermetically welded to the inner cylinder.

55 Within the envelope and at the upper end thereof, there is provided an anode I8, suitably constructed of a large block of graphite. This is insulatingly supported from the header l5 by means of a seal which includes an insulating part 20 and a metal cap 21. A metal sleeve 24 ex- 5 tending up into the insulator 20 serves to protect the joint between the insulator .and the header is from excessive electrostatic stress.

A supporting connection between the cap 21 and the anode is providedby means of a heavy 10 rod22 extending down into the interior of the envelope. The anode terminal is connected to an external source of potential (not shown) by means of a stranded cable 23.

At the lower end of the envelope there is provided a pool-type cathode 26 which is in contact with the header Hi. This cathode may comprise a body of mercury or some other material, such as cadmium, which is capable of analogous use. A heavy conductor 32 secured to the bottom of the header provides a convenient terminal connection for the cathode.

In cooperative relation with the cathode surface there is provided a make-alive device exemplified as a tapered rod 21 of semi-conducting material supported in permanent contact with the cathode material This is provided with a lead-in conductor 28 which is insulated from the cathode material by means of a bead 30 of glass or other insulating material. In use the lead-in conductor is connected to a source of control potential adapted to render'the discharge device conductive at cyclically recurrent periods or at periods which are within the control of the operator. d

The usefulness in high voltage circuits of a device such as that so far described depends primarily on its ability to avoid arc-back occurrences. In the application Serial No. 191,855, previously referred to, it is pointed out that this 40 ability is materially enhanced by the use of cooled bafiie surfaces adapted to shield the anode from direct exposure to the cathode surface. My present invention constitutes an improvement over the aforesaid application in respect to the form and arrangement of the baifie elements.

According to my invention, these elements comprise a series of sheet metal members spaced axially along the discharge path and supported directly from the lateral wall of ,the envelope. In the preferred embodiment illustrated in Fig. 1, for example, they are constituted of metal halfdisks 34, 35 and'36 whose curved peripheral portions are provided with flanges 34, 35 and 36. These engage the inner wall surface of the envelope and are preferably integrally welded thereto. This arrangement, which is an exceptionally convenient and economical one from the manufacturing standpoint, helps to maintain the bafile surfaces relatively cooly' by conveying heat from such surfaces to the cooling fluid in the outer jacket.

Since the cathode spot always originates in the vicinity of the make-alive electrode 21, it is preferable to dispose the lowest bafiie 34 directly over this electrode. In this way, material which is splashed upward by the agitation produced in the vicinity of the cathode spot is effectively intercepted. The other baflles 35 and 36 are distributed about the circumference of the envelope in such a way as to shield the anode from the cathode end of the tube and to provide a tortuous path for the discharge current. As appears most clearly in Fig. 2, these baflies are of such dimensions as to overlap one another slightly.

While the beneficial operation of a baffle system such as that disclosed is not fully understood, it is assumed that it is due primarily to the action of the baffle members in preventing passage of splashed or vaporized material into the region of the anode. The overlapping relationship of the baflles obviously tends to prevent liquid particles from reaching the anode surface while the fact that the discharge current is caused to traverse an irregular path apparently lessens the amount of vapor swept into the upper part of the envelope. Whatever the explanation, a very marked improvement in operation is obtained as is evidenced by the following tabulation of the comparative results obtained with various numbers of bafiles under similar test conditions:

1. No battles-arc-back occurs at 2000 volts.

2. Two bafiles--arc-back occurs at 9000 volts.

3. Three bafiles-arc-back occurs at about 30,000 volts.

The increase in arc-back resistance noted is obtained at the cost of an increase in the normal arc drop through the discharge space, which drop may be as high as 25 volts with three baffles. However, this is a factor which is of minor importance in connection with most high voltage applications.

The precise arrangement of the parts so far described is in no way essential to the purposes of my invention and in Fig. 3 I have shown an alternative embodiment. In this case, as in that previously described, the envelope comprises a pair of concentric metal tubes 40 and 4|. An anode is indicated at 43 and a pool-type cathode at 44. The make-alive device comprises an arrangement such as is described and claimed in L. D. Miles application Serial No. 168,197, filed October 9, 1937. It includes a shielding enclosure 45 within which are provided a make-alive electrode 46 and a pair of holding anodes 41 and 48. After the device is initially started by application of potential to the electrode 46, the holding anodes are energized alternately so as to maintain a continuous cathode spot. This cathode spot is normally held within the confines of the shielding enclosure, but may divide in the event of the application of a positive potential to the anode 43 so as to permit the establishment of another cathode spot on the unconfined surface of the cathode. This cathode spot division is permitted by means of narrow slots 50 which are provided in the enclosing shield at the surface of the cathode. A series of lead-in connections 52 permit the necessary energization of the electrodes 46, 41, and 48.

The bafile system shown in Fig. 3 comprises an upper sheet metal member 54 which is of generally arcuate form, and which has a depending fiange 55 secured to the inner wall surface of the envelope so as to be in good heatexchanging relation therewith. The lower baflle 56, on the other hand, is of such shape as to be complementary to the baffle 54. That is to say, it extends across that portion of the discharge path which is not covered by the upper baflle. It slightly overlaps the upper bafile as is indicated in Fig. 4. In the appended claims the term circular segment is intended to apply either to the bafiie shapes shown in Fig. 2 or to those shown in Fig. 4. As so used, it designates generically any segmental member which has a peripheral portion of circular arcuate form, but which is of substantially less area than would be subtended by a complete circle of similar radius.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high voltage, high current rectifier including a cylindrical metal envelope, an anode supported at one end of the envelope, a pooltype cathode at the other end of the envelope, and a series of axially spaced metal baflles in the form of circular segments interposed between the anode and cathode, the curved peripheral portions of said baiiles being provided with flanges which engage the inner wall surface of the envelope in good heat-exchanging relation therewith, and the various baflles being positioned at diilerent circumferential portions of the envelope so that they serve conjointly to shield the anode from any direct exposure to the cathode.

2. A high voltage, high current rectifier including an elongated cylindrical envelope, an anode supported at one end of the envelope, a pool-type cathode at the other end of the envelope and a series of axially spaced baiiles in the form of circular segments interposed between the anode and cathode and extending inwardly from the envelope wall, the curved peripheral portions of said baffles being shaped to interfit with the inner wall surface of the envelope in good heat-exchanging relation therewith and the. various bafiles being positioned at different circumferential regions of the envelope so that they serve conjointly to shield the anode from any direct exposure to the cathode.

3. An electrical discharge device including the combination of an elongated cylindrical metal envelope enclosing a single main anode, a pooltype cathode spaced from the anode, a makealive device for cyclically initiating a cathode spot at a region adjacent to the outer periphery of the cathode, a first baffle extending inwardly from the envelope wall so as directly to overlie the said region of the cathode, the said bafiie member being a circular segment of area approximately equal to half the cross-section of the envelope, and a second baille displaced from the first balile axially of the envelope, the said second baffle also being a circular segment of area approximating that of the first baille and being circumferentially displaced therefrom so that the two baffles serve conjointly to shield the anode from direct exposure to the cathode.

JOHN H. HUTCHINGS. 

